Electric protective system and apparatus



May 16, 1939- SpHORIKOSHl ELECTRIC PROTECTIVE SYSTBI AND APPARATUS Pig. 2.

Filed Nov. 24,

Inventor I Shinichiro H rikoshi, 5 Hi Attorney.

Patented May 16, 1939- PATENT OFFICE ELECTlilC PROTECTIVE SYSTEM AND APPARATUS Shinichiro Horikoshi, Tokyo, Japan, assignor to General Electric Company, a corporation of New York Application November 24, 1937, Serial No. 176,320 In Japan November 28, 1936 14 Claims.

The present invention relates to electric protective systems, and has for an object the provision, in an electric protective system embodying a lightning arrester, of means for protecting the arrester from continuous current of commercial power frequencies without detracting from the operation of the arrester on lightning surges.

In the practice .of the invention, a fuse is connected in series with the lightning arrester to protect the arrester against continuous abnormal voltages such, for example, as may occur due to arcing grounds. It is desirable that the fuse remain intact upon subjection of the arrester circuit to a lightning surge current of several thousand amperes for only a few micro-seconds and that the fuse operate, or fuse, upon subjection of the arrester circuit to commercial frequency current, of considerably smaller but abnormal value, which is continuous over a period of approximately 0.1 second or longer. There are some conditions under which such desired operation can not be'satisfled by the fuse alone. Hence, in accordance with the present invention, an inductive coil or other suitable device is connectedin series with the fuse for producing impedance in the fuse circuit and a special spark gap is connected in parallel with the fuse circuit comprised of the fuse and impedance producing device, the

arrangement being such that when the arrestercircuit is subjected to a current of steep wave front, such as a lightning surge current, the greater part of the current discharges across the sparkgap and passes to the arrester for operation of the latter in its normal manner, while with a continuous abnormal current of ordinary frequency, the current passes through the fuse and impedance device and ruptures the fuse, thus preventing damage to the lightning arrester.

That which I believe to be novel and my invention will be better understood from the following description and the claims appended thereto, taken in conjunction with the accompanying drawing in which Fig. 1 illustrates schematically a protective system embodying the present invention and Fig. 2 illustrates diagrammatically and in section one form of apparatus for carrying out the invention.

Referring to Fig. 1, H designates a transmission or feeder line which is connected to ground through a lightning arrester conventionally shown at l2. In series with the arrester there is connected a fuse l3 and an inductive coil II, and in shunt with the fuse and coil is connected a spark gap having discharge electrodes i5. With this arrangement, relatively continuous abnormal current of commercial frequency imposed upon the arrester circuit will pass through the fuse and melt the same, the inductive coil offering relatively little impedance to current of commercial frequency. The melting of the fuse clears the lightning arrester and prevents damage thereto. On the other hand, when the arrester circuit is subjected to lightning surge current, the inductive coil offers high impedance thereto and the impedance drop across theinductive coil and fuse will result in arc-over between electrodes l5, thus short-circuiting the fuse and causing passage of the current through the arrester which functions in its normal manner.

It is desirable that some means be provided for drawing the electrodes of the spark gap apart to a circuit interrupting distance upon rupture of the fuse. One method of accomplishing this is illustrated diagrammatically in Fig. 2 wherein the fusible element I3 is shown as being disposed in an expulsion chamber formed by a casing l6 of insulating material, which casing has mounted on the end thereof a metal terminal block l1 pro vided with a central opening 18 for the outward passage therethrough of the connection lead i9 of. the fuse. Lead I9 is connected in any suitable manner to line H. The series connected inductive coil H is illustrated diagrammatically as being mounted within casing IS in surrounding relation to the fuse, although the coil may if desired be mounted exteriorly of the casing. A discharge gap A, in parallel with the fuse and inductive coil is provided by the connection lead I! and the inner wall of terminal block 11 which forms opening l8, and the terminal block is connected to lightning arrester I2 through lead 20. With this last described arrangement, the termi-' nal or connection lead I9 is expelled from the opening l8 upon rupture of the fuse, in the well known manner of expulsion fuses. Since lead l9 forms one of the electrodes of gap A, this outward expulsion of the lead results in increasing the gap substantially to infinity so that no current may flow thereafteracross the gap and the arrester is effectively removed from the circuit so that no damage may be done to the arrester by continuous abnormal current of commercial power frequency. In case a. spring is employed fortensioning the fuse link and effecting rapid separation of the fuse link terminals on fuse operation, as is relatively common practice, the tensioning spring will of course aid in effecting separation of the gap electrodes.

Thus the present invention; provides a protective system wherein a discharge gap is so combined with a fuse and an inductive coil or other suitable impedance providing device that transient currents pass, without damage to the fuse, through the gap to the arrester which then operates in its intended manner, while the fuse operates only upon continuous abnormal current of commercial power frequency to disconnect the arrester and prevent damage thereto.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electric protective system including a lightning arrester, protective means for said arrester including a pair of circuits connected in series with the arrester and in parallel with each other, one of which circuits includes a fuse and the other of which circuits includes a discharge gap, said one circuit having substantial impedance whereby the impedance drop thereacross upon subjection of the said one circuit to lightning impulse current will cause arc-over of said gap to by-pass the surge current around the fuse without damage to the latter, said fuse being arranged to operate upon subjection of said one circuit to commercial frequency current of predetermined abnormal value.

2. In an electric protective system including a lightning arrester, a fuse connected in series with said arrester for protecting the latter against abnormal currents of commercial frequency, and means for protecting said fuse against lightning surge currents including an impedance device connected in series with said fuse and a discharge gap connected in parallel with said fuse and impedance device.

3. In an electric protective circuit including a lightning arrester, a fusible conductor connected in the circuit in series with the arrester, a surge gap connected in parallel with a part of the circuit including said fusible conductor and in series with the arrester for by-passing lightning impulse currents around said fusible conductor to the arrester, means operatively associated with said part of the circuit for producing thereacross a voltage drop sufficient to cause arc-over of said gap upon subjection of the circuit to lightning impulses, and means including said fusible conductor operative to interrupt the circuit to the arrester in response to flow of abnormal current of power frequencies.

4. In combination, an electric protective circuit including a lightning arrester; a part of said circuit, connected in series with the arrester, in-

cluding a fusible conductor and having substantial inductance; a surge gap connected in parallel with said part of the circuit and in series with the arrester, which said gap is arranged to sparkover upon subjection of the circuit to lightning impulses so as to by-pass lightning impulse currents around said fusible conductor to the arrester, and means including said fusible conductor operative to interrupt the circuit to the arrester upon subjection of the circuit to abnormal current of power frequencies.

5. In an electric protective system including a lightning arrester, a pair of circuits connected in series with said arrester and in parallel with each other, one of which circuits includes a fuse and has substantial impedance and the other of which circuits includes a discharge gap having relatively movable electrodes, and means operative responsively to operation of said [use for effecting relative movement apart of said electrodes to increase said gap.

6. In combination, an electric protective circuit including a lightning arrester; a part of said circuit, connected in series with the arrester, including a fusible conductor and inductive means serially connected therewith; a surge gap connected in parallel with said fusible conductor and inductive means and in series with the arrester, said gap having relatively movable electrodes and being arranged normally to by-pass lightning impulse currents around said fusible conductor to the arrester, and means operative to effect relative movement apart of said electrodes to circuit interrupting distance upon rupture of said fusible conductor.

7. In an electric protective circuit including a lightning arrester, circuit interrupting means connected in the circuit in series with the arrester and operable responsively to abnormal current of power frequencies for interrupting the circuit to the arrester, a gap connected in parallel with a part of the circuit including said interrupting means and in series with the arrester, said gap including a pair of relatively movable electrodes and being arranged normally to bypass lightning impulse currents around said interrupting means to said arrester, said part of the circuit including means operative to produce thereacross a voltage drop sufficient to cause arcover of said gap upon subjection of the circuit to lightning impulses, and means operative to effect relative movement apart of said gap electrodes to a circuit interrupting distance upon operation of said circuit interrupting means.

8. In an electric circuit, the combination of means to be protected, means providing an inductive current conducting path connected in series with said means to be protected and including a fusible conductor, a surge gap connected in parallel with said inductive path and in series with said means to be protected, said gap including a pair of relatively movable electrodes and being arranged normally to by-pass lightning impulse currents around said fusiblc conductor, and means operative to effect relative movement apart of said electrodes to circuit interrupting distance upon operation of said fusible conductor.

9. In an electric circuit including means to be protected, circuit interrupting means connected in the circuit in series with said means to be protected and operable responsively to abnormal current for interrupting the circuit to said means to be protected, a surge gap connected in parallel r' with a part of the circuit including said interrupting means and in series with said means to be protected, said gap including apair of relatively movable electrodes and being arranged normally to by-pass lightning impulse currents around said interrupting means, said part of the circuit including means operativeresponsively to rate of change of current in the circuit for producing across said gap a voltage drop sufficient to cause arc-over of the gap upon subjection of the circuit to lightning impulses, and means operative to effect relative movement apart of said gap electrodes to a circuit interrupting distance upon operation of said circuit interrupting means.

10. Electric protective apparatus comprising in combination, means providing an inductive-current conducting path including a fusible conductor, a surge gap connected in parallel with said inductive path and including a pair of relatively'movable electrodes, said gap being arranged normally to protect said fusible conductor by bypassing lightning impulse currents around the fusible conductor and the fusible conductor being arranged to interrupt abnormal current of power frequencies, and means operative to effect relative movement apart of said electrodes upon operation of said fusible conductor.

11. Electric protective apparatus comprising in combination a fusible conductor, inductive means in series with said fusible conductor, a surge gap connected in shunt directly across said fusible conductor and inductive means for by-passing lightning impulse currents around the fusible conductor, at least one of the electrodes of said gap being movable relative to the other of the electrodes, and means operative to effect relative movement apart of said electrodes upon rupture of the fusible conductor.

12. In an electric protective apparatus, a circuit having substantial impedance and including a fuse, a second circuit connected in parallel with said first circuit and including a discharge gap having a pair of relatively movable electrodes, and means operative responsively to rupture of said fuse for effecting relative movement apart of said electrodes to increase said gap.

13. In an electric protective apparatus, a circuit having substantial impedance and including a fusible element with fuse terminals one of which is supported for movement relative to the other of the terminals, means providing an expulsion chamber surrounding said fusible element and having a discharge opening for the expulsion therethr'ough of said one terminal upon fuse operation, and a second circuit connected in shunt with said first circuit and including a discharge gap having a pair of electrodes one of which is supported for movement away from the other of the electrodes to increase said gap in response to expulsion of said one electrode from said opening.

14. An electric protective apparatus including in combination, a conductor having a fusible section, a housing providing an expulsion chamber in surrounding relation to said fusible section, a surge gap connected in parallel with a part of said conductor including said fusible section, said gap including an electrode supported in substantially fixed relation to said housing and a second electrode supported by said conductor in cooperative spaced relation to said first electrode, and inductive means arranged to produce across said gap a voltage drop sufficient to cause arc-over of the gap upon subjection of said conductor to lightning impulse currents, said second electrode being arranged for movement away from said first electrode to increase said gap upon operation of said fusible section.

SHINICHIRO HORIKOSHI. 

